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We assume that the electrons would fill the molecular orbitals of molecules like electrons fill atomic orbitals in atoms. Determine the total number of electrons in the molecule. Fill the molecular orbitals from bottom to top until all the electrons are added. Describe the electrons with arrows. Put two arrows in each molecular orbital, with the first arrow pointing up and the second pointing down The molecular orbitals are filled in a way that yields the lowest potential energy for the molecule. The maximum number of electrons in each molecular orbital is two. (by following the Pauli exclusion principle.) Orbitals of equal energy are half filled with parallel spin before they begin to pair up. (by following Hund's Rule.) The expected molecular orbital diagram from the overlap of 1s, 2s and 2p atomic orbitals is as follows.  Like for hydrogen, the 1s from one atom overlaps the 1s from the other atom to form a σ1s bonding molecular orbital and a σ*1s antibonding molecular orbital. We describe the stability of the molecule with bond order. bond order = 1/2 (#e- in bonding MO's - #e- in antibonding MO's) We use bond orders to predict the stability of molecules. If the bond order for a molecule is equal to zero, the molecule is unstable. A bond order of greater than zero suggests a stable molecule. The higher the bond order is, the more stable the bond. We can use the molecular orbital diagram to predict whether the molecule is paramagnetic or diamagnetic. If all the electrons are paired, the molecule is diamagnetic. If one or more electrons are unpaired, the molecule is paramagnetic. for more information visit crest science academy